G.fast is an ITU (International Telecommunication Union) DSL (digital subscriber line) standard, and provides ultra-high-speed broadband network transmission. The service distance of G.fast is within 300 m, which provides a solution to the last mile problem for broadband networks. Therefore, in places where optical fiber deployment is difficult, G.fast can achieve ultra high bandwidth and speed. For example, the network transmission speed of the copper telephone wire in an old traditional building can be increased up to 1 Gbps. The G.fast system does not require rewiring the entire building or house. Thus, the most expensive and time-consuming process for connecting the optical fiber to residences can be eliminated. At the same time, the coaxial cable is already installed widely in the field as an existing cable TV (CATV) and broadband service. The existing equipment for telecommunications companies may be a copper telephone wire providing plain old telephone service (POTS) to homes and a coaxial cable providing CATV service. Since the coaxial cable is owned by the community management committee, there won't be a property problem when the telecommunications company uses it. Furthermore, because of the digitization of cable TV, the telecommunications company can also use the coaxial cable to provide G.fast service.
ITU Recommendation (ITU-T G9701) requires reverse power for G.fast distribution point unit (DPU)/digital subscriber line access multiplexer (DSLAM) equipment connected to a dwelling. The telecommunications company may keep the copper telephone wire to provide POTS, and find an alternative interface to feed power from the dwelling of a subscriber to the CO (central office) interface of the G.fast DPU/DSLAM equipment to provide G.fast service. For example, the dwelling of the subscriber may have a cable interface as well as the copper interface. Both the copper interface and the cable interface are examples of generic interfaces. But crosstalk occurs between the G.fast system and an existing transmission line (e.g., CATV) on the same generic interface.
Please refer to FIG. 1, which shows an installation scenario 100 for installing CATV and G.fast system on generic interfaces and removing crosstalk. The left side of installation scenario 100 is a distribution point, and the right side is a house. FIG. 1 shows a G.fast DPU/DSLAM equipment 101 which has many ports. Some of the ports of the G.fast DPU/DSLAM equipment 101 (4 ports are shown in FIG. 1) are each connected to an individual unit of G.fast customer premises equipment (CPE) 102. The other side of the G.fast DPU/DSLAM equipment 101 is connected to an optical fiber or an optical line terminal (OLT) 105, and is connected to the Internet 108 through a cloud 120, a video on demand server 107 and an element management system (EMS) server 106 via the optical fiber or an optical line terminal (OLT) 105. Each of the ports of G.fast DPU/DSLAM equipment 101 receives signals from the individual unit of the G.fast CPE 102 that connected to its port. The G.fast DPU/DSLAM equipment 101 detects which generic interface the signals come from and connects the port to the generic interface, e.g., the copper interface or the cable interface. The telecommunications company may select different generic interfaces when providing different types of G.fast services, e.g., Internet access or video on demand. If a TV signal comes from a floor distribution box 104, the TV signal goes to a splitter 109 which integrates CATV, G.fast and power, and which connects to another splitter 110 in the house. The splitter 110 separates CATV from the G.fast CPE 102, and the video signal shows on TV 103. Some ports of the G.fast DPU/DSLAM equipment 101 may be connected to copper interfaces, and very-high-bit-rate digital subscriber lines (VDSLs) may have been installed on the copper interfaces. Crosstalk also occurs between VDSL and G.fast.
In addition, because the G.fast DPU/DSLAM equipment is installed after the installation of an existing transmission line, such as VDSL or CATV, it is mandatory to remove crosstalk interference between G.fast and the existing transmission line when the G.fast DPU/DSLAM equipment is installed. The interference from the existing transmission line causes the transmission speed to be dropped, the packet to be lost, and even worse, the interference causes the G.fast link to go down.
G.fast has two profiles corresponding to bandwidths (maximum frequencies) of 106 MHz and 212 MHz. The frequency for analog CATV is above 54 MHz, and the frequency for digital CATV is above 77 MHz. Therefore, taking G.fast 106 MHz profile as an example, crosstalk may occur between G.fast and analog CATV in the frequency range between 54 MHz and 106 MHz, and between G.fast and digital CATV in the frequency range between 77 MHz and 106 MHz.
VDSL has many profiles, e.g. 8a, 8b, 8c, 8d, 12a, 12b, 17a and 30a, each with its own bandwidth. Among them, 30a has the largest bandwidth (highest maximum frequency) of 30 MHz. The existing VDSL services on a bundle of wires may include one or more of the profiles above. Crosstalk may occur between G.fast and the existing VDSLs having various bandwidths.
Because data is modulated using discrete multitone (DMT) modulation in G.fast, there are 2048 subcarriers (i.e. 2048 tones or frequencies, where each tone or frequency has a sequential index) for the 106 MHz profile and 4096 subcarriers for the 212 MHz profile. The spacing between adjacent subcarriers is 51.75 kHz. ITU Recommendation (ITU-T G9700) requires that the G.fast system should be equipped with a set of tools called a power spectral density (PSD) mask, which can be configured to deal with the problem of crosstalk interference between G.fast and existing transmission lines. For example, some of the G.fast subcarriers can be masked to remove crosstalk. In the case of the copper interface where G.fast and VDSLs are installed on the same bundle of wires, the PSD mask can be configured to set a start frequency in the G.fast system so that the frequency range of the G.fast system lies outside of all the existing VDSLs on the bundle of wires which cause crosstalk, and thus crosstalk is removed automatically.
In prior art, a technician installing the G.fast DPU/DSLAM equipment uses the PSD mask to manually filter out frequencies at which crosstalk occurs between a port of the G.fast DPU/DSLAM equipment and existing transmission lines for each port. For the convenience of the installation technician, the G.fast DPU/DSLAM equipment's manufacturer usually provides the G.fast DPU/DSLAM equipment with the following functions: measuring a type of loop diagnostic metric data related to a communication loop connected between a port of the G.fast DPU/DSLAM equipment and the CPE, e.g., signal-to-noise ratio (SNR), and showing the loop diagnostic metric data to the installation technician, so as to determine the G.fast subcarriers to be masked for that port. Therefore, the installation technician has to be able to read the loop diagnostic metric data, determine the G.fast subcarriers to be masked based on the loop diagnostic metric data, and manually send the correct instructions to mask those G.fast subcarriers using his knowledge of the G.fast system and equipment. However, typical installation technicians do not have these abilities. Experienced technicians with these abilities have to be dispatched, leading to high operation costs. However, even for experienced technicians with these abilities, under the condition that the only crosstalk exists between VDSL and G.fast, the average installation time of a unit of the G.fast DPU/DSLAM equipment is about two days. The lengthy installation time is detrimental to the promotion of G.fast, not to mention that manual operations may introduce misjudgments, e.g., in determining the G.fast subcarriers to be masked, or in sending the instructions to mask those G.fast subcarriers. Therefore, an invention which can greatly speed up the installation time and facilitate the correct installation by typical installation technicians is urgently needed.
A patent application (WO 2015/150732 A1) presented a method and an apparatus for allocating resources in a Digital Subscriber Line (DSL) network on the copper interface, the network includes at least one lower-tier digital subscriber line carrying signals according to a first protocol between a transceiver device at a lower-tier network node and a subscriber transceiver device and further includes at least one higher-tier digital subscriber line carrying signals according to a second protocol between a transceiver device at a higher-tier network node and a subscriber transceiver device, wherein the first protocol permitting signals to be carried at frequencies in a range having a higher upper limit than the second protocol. Thus WO 2015/150732 A1 is applicable to crosstalk between a lower-tier digital subscriber line like G.fast and a higher-tier digital subscriber line like VDSL in the running mode. FIG. 3 of WO 2015/150732 A1 discloses an exemplary process. From FIG. 3 and the related part of the specification of WO 2015/150732 A1, it can be seen that a scan of quiet line noise (QLN) starting from a highest frequency is performed, the most efficient way of performing the scan being sequential from the highest frequency down to the lowest frequency, and a minimum frequency (i.e., start frequency mentioned above) in the lower-tier digital subscriber line is determined by a degradation criterion based on the QLN corresponding to a single specific frequency. The technique is applicable only to the copper interface. Moreover, misjudgement may occur due to the degradation criterion based on the QLN corresponding to a single specific frequency. Furthermore, according to the specification, tones of frequencies above the range that may be used for the longer lines (i.e., the higher-tier digital subscriber lines) may be ignored in choosing the highest frequency. Without adding a guard band to the highest frequency, misjudgement may also occur due to intersymbol interference (ISI).
In order to overcome the drawbacks in the prior art, a method and an apparatus for automatically removing crosstalk is disclosed.